<?php
/**
 * datetime: 2021/9/8 15:52
 * user    : chenlong<vip_chenlong@163.com>
 **/


namespace weChat\apiv3;

/**
 * Class AesUtil
 * @package weChat\apiv3
 * @author chenlong<vip_chenlong@163.com>
 * @date 2021/9/8
 */
class AesUtil
{
    /**
     * AES key
     *
     * @var string
     */
    private $aesKey;

    const KEY_LENGTH_BYTE = 32;
    const AUTH_TAG_LENGTH_BYTE = 16;

    /**
     * Constructor
     */
    public function __construct($aesKey) {
        if (strlen($aesKey) != self::KEY_LENGTH_BYTE) {
            throw new \InvalidArgumentException('无效的ApiV3Key，长度应为32个字节');
        }
        $this->aesKey = $aesKey;
	}

    /**
     * Decrypt AEAD_AES_256_GCM ciphertext
     *
     * @param string    $associatedData     AES GCM additional authentication data
     * @param string    $nonceStr           AES GCM nonce
     * @param string    $ciphertext         AES GCM cipher text
     *
     * @return string|bool      Decrypted string on success or FALSE on failure
     */
    public function decryptToString($associatedData, $nonceStr, $ciphertext) {
        $ciphertext = \base64_decode($ciphertext);
        if (strlen($ciphertext) <= self::AUTH_TAG_LENGTH_BYTE) {
            return false;
        }

        // ext-sodium (default installed on >= PHP 7.2)
        if (function_exists('\sodium_crypto_aead_aes256gcm_is_available') && \sodium_crypto_aead_aes256gcm_is_available()) {
            return \sodium_crypto_aead_aes256gcm_decrypt($ciphertext, $associatedData, $nonceStr, $this->aesKey);
		}

        // ext-libsodium (need install libsodium-php 1.x via pecl)
        if (function_exists('\Sodium\crypto_aead_aes256gcm_is_available') && \Sodium\crypto_aead_aes256gcm_is_available()) {
            return\ Sodium\crypto_aead_aes256gcm_decrypt($ciphertext, $associatedData, $nonceStr, $this->aesKey);
		}

        // openssl (PHP >= 7.1 support AEAD)
        if (PHP_VERSION_ID >= 70100 && in_array('aes-256-gcm', \openssl_get_cipher_methods())) {
            $ctext = substr($ciphertext, 0, -self::AUTH_TAG_LENGTH_BYTE);
            $authTag = substr($ciphertext, -self::AUTH_TAG_LENGTH_BYTE);

            return openssl_decrypt($ctext, 'aes-256-gcm', $this->aesKey, \OPENSSL_RAW_DATA, $nonceStr,
				$authTag, $associatedData);
		}

        throw new \RuntimeException('AEAD_AES_256_GCM需要PHP 7.1以上或者安装libsodium-php');
    }
}
